By: Thomas H. Welby Thomas H. Welby Published: September 2005

Safety Policy: Deceptive Dangerous: Cave-Ins and Other hazards in Trenches and Excavations (Part 1 of 2)

The risks to life and safety posed by unsafe excavation and trenching work at construction sites are under-appreciated. Foresight in this area is critical: when cave-ins occur, even in shallow trenches, workers can be trapped in an instant, and suffocated by the tremendous force of a load of dislodged earth.

Studies show that excavation safety compliance is often lax on small jobs, performed by smaller companies. Many injuries and deaths occur when workers go down into insufficiently-shored trenches or excavations, intending to work there for only a brief period. Plumbers and others are often afflicted with over-confidence, as they do so much below-ground work, usually without incident. Their bravado, however, should be discouraged, as cave-ins can happen swiftly. The weight of collapsed earth and, often, tight access to the site of a cave-in, make successful rescues the exception rather than the rule. Indeed, workers attempting to rescue colleagues in cave-ins are themselves often injured, and occasionally killed. A cubic yard of earth can weigh a ton and a half or more, and every time a trapped worker exhales, the weight of the load makes it harder to inhale the next breath.

OSHA initiated a special emphasis program for trenches and excavations in 1985, and revised its trench and excavation standards in 1989. A study published in the Journal of Occupational and Environmental Medicine showed that OSHA’s revised standard, and a targeted inspection program that began in 1990, sharply reduced fatality rates from cave-ins. Indeed, looking just at construction industry fatalities, deaths from other causes dropped about 28% in the 10-year period that ended in 1995, but deaths in cave-ins fell approximately 50%.

While the same study was hesitant to draw conclusions concerning the relationship between deaths in construction site cave-ins, and company size and union versus non-union status, it’s clear that OSHA inspections are more frequent at large companies and jobsites, and that non-union death rates from cave-ins are roughly double those for union workers. What this indicates is that OSHA regulations are highly effective in reducing risks associated with trenches and excavations, but only if workers are sufficiently trained, and employers enforce the standards. Workers and employers both are far too often casual about safety in trenches and excavations. Following three cave-in deaths in an eight-month period in the Pittsburgh area last year, one safety official (representing management) estimated that only 20% of the people working in trenches are properly protected. If they could meet and talk with a former plumber or other worker living with severe, lifelong and disabling injuries, sustained in the blink of an eye when soil collapsed on him exerting pressure of up to 100 pounds per square inch, perhaps they would be more careful.

In this month’s installment, Welby “the Engineer” will run through some of OSHA’s basic precepts concerning excavations, trenches and associated safety issues. In next month’s follow-up piece, Welby “the Construction Lawyer” will discuss some court decisions, in which trenching cave-ins and related hazards have been dealt with.

Although falls, electrocution, falling objects (or a backhoe) and bad air (which can poison workers, or result in fires) pose additional risks in trenches, the primary danger is from cave-ins. These occur when the soil forming the side of the excavation can no longer resist the forces being applied to it. This results from a reduction in the frictional and cohesive capacities of the soil to resist forces. Freezing and thawing, or the addition or removal of water from the pores of the soil, are frequent causes in reducing the soil’s ability to resist forces. Dynamic loads from vibrations caused by pile driving or other construction operations, or even nearby railroad or vehicular traffic, can have the same effect.

An “excavation” under OSHA means “any man-made cut, cavity, trench or depression in an earth surface, formed by earth removal.” A “trench” is a sub-species of excavation, generally, a narrow excavation below the surface of the ground, not more than 15’ wide at the bottom.

The most widely-used protective systems include support systems, sloping and benching systems, and shield systems, a/k/a trench boxes.

Before opening an excavation, the approximate locations of utility installations (sewer, telephone, fuel, electrical, water lines or other underground installations) are required to be determined. While beyond the scope of this article, these determinations present significant technical challenges and are often unreliable, generally as most detection technologies can’t locate lines that are neither metallic, nor installed with ferrous or other magnetic markers attached, to enable them to be found. Major utilities, of course, can usually provide reliable information, but surprise encounters with PVC or other difficult-to-detect underground installations are not uncommon.

Excavations must be inspected daily prior to the start of work, and as needed throughout the shift. Inspections must also be made after every rainstorm or other “hazard-increasing occurrence” if employee exposure can be reasonably anticipated. A “competent person,” defined generally as one capable of identifying existing and predictable hazards and unsanitary, hazardous and dangerous conditions, and having authority to take measures to eliminate them, is to perform such inspections.

OSHA requires employers to train workers about excavation hazards, and how to protect themselves. Video and other safety instruction materials, of varying quality, are available from a number of sources, but while the following is not a complete or sufficient “course of instruction,” a few of the most basic rules need to be repeated, and repeated often. “Before you work in a trench,” workers should be told, “get a ‘competent person’ to approve it.” Equipment (such as ventilators and water pumps) should be checked. The trench should have all electricity, gas and water pipes shutoff, and booms should never be used near overhead power lines (unless the “competent person” has first ascertained that the power has been cut off, and the lines have been grounded).

If “bad air” is expected, a “competent person” must test the air to ensure that the air has between 19.5% to 23.5% oxygen. Gasoline, methane, or other substances that can burn or explode should be at less than 20% of the lower explosive or flammability limit. The air should also be checked for toxins like chlorine, carbon monoxide, sewer gases, and hydrogen sulfide. These toxins can kill, and it is the “competent person’s” job to ascertain if blowers can keep the air safe, if any such substances are present. If “bad air” is anticipated, there must be a rescue plan, and rescue equipment present on-site. Rescue teams must have special training.

OSHA classifies soils as stable rock, or type A, type B, or type C soil. Stable rock, and type A soils are the safest. Most soils are type B. Sand, and trenches with water, are type C soils. Water in a trench is a “red flag” of possible danger. Clay soils can be of type A, B, or C, depending on how much water is in the clay. Testing is imperative, because cave-ins occur with alarming frequency in clay soils, because they look safe.

Protective systems — usually, sloping, benching, shoring, or a trench box — must be in place whenever workers are down in a trench. If a trench is 4 feet deep or more, there must be ladders within 25 feet of all persons who will be working in the trench. The spoil pile must be kept a minimum of 2 feet from the edge of the trench. Rocks, soil or other materials must be prevented from falling into the trench. Barriers should be used, if needed.

If a trench caves in, “911” or other emergency services should be summoned at once. If co-workers can be assisted from outside the trench, fine, but no one should go down into a trench that is caving in, or that has bad air, even to rescue a fellow worker. Such rescue attempts usually fail, and the would-be rescuers can be injured or killed.

Every construction contractor, of course, is conscious of the costs of OSHA compliance, and aware that faster work increases profit margins. However, few things that occur on construction sites are more terrible than a workforce watching helplessly, as a colleague trapped by a trench cave-in suffocates and expires under tons of soil. In addition to the destruction of life and morale, the financial costs of trenching accidents can be huge. They include work stoppage to rescue the victim, time and labor to re-excavate the collapsed trench, workers’ compensation costs, increased insurance premiums, and paperwork and management time lost in connection with the investigation of the accident. OSHA fines for willful and serious violations of excavation standards , and the employer may be exposed to liability for wrongful death, personal injury, and conscious pain and suffering as well.

The combination of potential fines, loss of human life, lawsuits, increases in already high insurance costs, and poor public relations can put a thriving construction company, especially those smaller ones that are subject to increased pressures to cut corners with regard to safety, out of business.

In short, it’s a great idea to bite your lip and write that check for the trench-box rental. It’s well worth the investment. Most of what goes into OSHA compliance, generally, is in the nature of sound planning and organization, not large cash outlays. Properly organized, worker safety instruction and enforcement should not cost employers greatly in lost time and profit — and the downside in shortchanging these efforts can be damaging, even fatal, to your business.

Next month, we’ll discuss some of the cases in which cave-ins and excavation hazards have been addressed.

Thomas H. Welby is a licensed professional engineer, as well as an attorney and managing partner of Welby, Brady & Greenblatt, LLP, a construction law firm with its main office in White Plains. Articles in this series are for general guidance only, and should not be relied upon as providing all information necessary for compliance with OSHA and other legal requirements.

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